//                                               -*- C++ -*-
/**
 *  @brief The class building chaos expansions
 *
 *  Copyright 2005-2025 Airbus-EDF-IMACS-ONERA-Phimeca
 *
 *  This library is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this library.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
#include <cstdlib>
#include <map>

#include "openturns/FunctionalChaosAlgorithm.hxx"
#include "openturns/OSS.hxx"
#include "openturns/PersistentObjectFactory.hxx"
#include "openturns/Point.hxx"
#include "openturns/FunctionImplementation.hxx"
#include "openturns/ComposedFunction.hxx"
#include "openturns/DatabaseFunction.hxx"
#include "openturns/FixedStrategy.hxx"
#include "openturns/CleaningStrategy.hxx"
#include "openturns/FixedExperiment.hxx"
#include "openturns/LeastSquaresStrategy.hxx"
#include "openturns/Exception.hxx"
#include "openturns/ResourceMap.hxx"
#include "openturns/LinearEnumerateFunction.hxx"
#include "openturns/HyperbolicAnisotropicEnumerateFunction.hxx"
#include "openturns/OrthogonalUniVariatePolynomialFamily.hxx"
#include "openturns/OrthogonalProductPolynomialFactory.hxx"
#include "openturns/StandardDistributionPolynomialFactory.hxx"
#include "openturns/LeastSquaresMetaModelSelectionFactory.hxx"
#include "openturns/LARS.hxx"
#include "openturns/KFold.hxx"
#include "openturns/CorrectedLeaveOneOut.hxx"
#include "openturns/DistributionTransformation.hxx"
#include "openturns/SpecFunc.hxx"

BEGIN_NAMESPACE_OPENTURNS

typedef Collection<Function> FunctionCollection;

CLASSNAMEINIT(FunctionalChaosAlgorithm)

static const Factory<FunctionalChaosAlgorithm> Factory_FunctionalChaosAlgorithm;


/* Default constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm()
  : MetaModelAlgorithm()
  , adaptiveStrategy_(FixedStrategy(OrthogonalProductPolynomialFactory(), 0))
  , projectionStrategy_(LeastSquaresStrategy())
  , maximumResidual_(ResourceMap::GetAsScalar( "FunctionalChaosAlgorithm-DefaultMaximumResidual" ))
{
  // Nothing to do
}


/* Constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Sample & outputSample)
  : FunctionalChaosAlgorithm(inputSample, Point(inputSample.getSize(), 1.0 / inputSample.getSize()), outputSample)
{
  // Nothing to do
}


/* Constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Point & weights,
    const Sample & outputSample)
  : FunctionalChaosAlgorithm(inputSample, weights, outputSample, BuildDistribution(inputSample))
{
  // Nothing to do
}


/* Constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Sample & outputSample,
    const Distribution & distribution)
  : FunctionalChaosAlgorithm(inputSample, Point(inputSample.getSize(), 1.0 / inputSample.getSize()), outputSample, distribution)
{
  // Nothing to do
}


/* Constructor */
/* This one is big as it implements the automatic choice of
   AdaptiveStrategy/ProjectionStrategy based on ResourceMap keys */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Point & weights,
    const Sample & outputSample,
    const Distribution & distribution)
  : MetaModelAlgorithm(inputSample, weights, outputSample, distribution)
  , adaptiveStrategy_()
  , projectionStrategy_()
  , maximumResidual_(ResourceMap::GetAsScalar("FunctionalChaosAlgorithm-DefaultMaximumResidual"))
{
  const UnsignedInteger inputDimension = inputSample.getDimension();
  Collection< OrthogonalUniVariatePolynomialFamily > polynomials(inputDimension);
  for (UnsignedInteger i = 0; i < inputDimension; ++ i)
    polynomials[i] = StandardDistributionPolynomialFactory(getDistribution().getMarginal(i));

  const Scalar qNorm = ResourceMap::GetAsScalar("FunctionalChaosAlgorithm-QNorm");
  EnumerateFunction enumerate;
  if (std::abs(qNorm - 1.0) <= SpecFunc::Precision) enumerate = LinearEnumerateFunction(inputDimension);
  else enumerate = HyperbolicAnisotropicEnumerateFunction(inputDimension, qNorm);
  OrthogonalProductPolynomialFactory basis(polynomials, enumerate);

  const Bool sparse = ResourceMap::GetAsBool("FunctionalChaosAlgorithm-Sparse");
  if (sparse)
  {
    const String fittingAlgorithm(ResourceMap::GetAsString("FunctionalChaosAlgorithm-FittingAlgorithm"));
    if (fittingAlgorithm == "CorrectedLeaveOneOut")
      projectionStrategy_ = LeastSquaresStrategy(inputSample, weights, outputSample, LeastSquaresMetaModelSelectionFactory(LARS(), CorrectedLeaveOneOut()));
    else if (fittingAlgorithm == "KFold")
      projectionStrategy_ = LeastSquaresStrategy(inputSample, weights, outputSample, LeastSquaresMetaModelSelectionFactory(LARS(), KFold()));
    else
      throw InvalidArgumentException(HERE) << "Unknown fitting algorithm: " << fittingAlgorithm;
    LOGINFO(OSS() << "In FunctionalChaosAlgorithm, selected a sparse chaos expansion based on LARS and " << fittingAlgorithm);
  }
  else
  {
    projectionStrategy_ = LeastSquaresStrategy(inputSample, weights, outputSample);
    LOGINFO(OSS() << "In FunctionalChaosAlgorithm, selected a chaos expansion based on FixedStrategy");
  }

  // total basis size can be either parametrized via MaximumTotalDegree or BasisSize
  const UnsignedInteger maximumTotalDegree = ResourceMap::GetAsUnsignedInteger("FunctionalChaosAlgorithm-MaximumTotalDegree");
  const UnsignedInteger basisSize = ResourceMap::GetAsUnsignedInteger("FunctionalChaosAlgorithm-BasisSize");
  const UnsignedInteger totalSize = std::min(inputSample.getSize(), basisSize ? basisSize : enumerate.getBasisSizeFromTotalDegree(maximumTotalDegree));
  LOGINFO(OSS() << "In FunctionalChaosAlgorithm, selected a basis size of " << totalSize);
  adaptiveStrategy_ = FixedStrategy(basis, totalSize);
}


/* Constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Sample & outputSample,
    const Distribution & distribution,
    const AdaptiveStrategy & adaptiveStrategy)
  : FunctionalChaosAlgorithm(inputSample, Point(inputSample.getSize(), 1.0 / inputSample.getSize()), outputSample, distribution, adaptiveStrategy)
{
  // Nothing to do
}


/* Constructor */
/* This one forces the use of a basic LeastSquaresStrategy. Maybe we should
implement the same logic as when both the AdaptiveStrategy and ProjectionStrategy
are deduced from ResourceMap keys. */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Point & weights,
    const Sample & outputSample,
    const Distribution & distribution,
    const AdaptiveStrategy & adaptiveStrategy)
  : MetaModelAlgorithm(inputSample, weights, outputSample, distribution)
  , adaptiveStrategy_(adaptiveStrategy)
  , projectionStrategy_(LeastSquaresStrategy(inputSample, weights, outputSample))
  , maximumResidual_(ResourceMap::GetAsScalar( "FunctionalChaosAlgorithm-DefaultMaximumResidual" ))
{
  // Nothing to do
}


/* Constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Sample & outputSample,
    const Distribution & distribution,
    const AdaptiveStrategy & adaptiveStrategy,
    const ProjectionStrategy & projectionStrategy)
  : FunctionalChaosAlgorithm(inputSample, Point(inputSample.getSize(), 1.0 / inputSample.getSize()), outputSample, distribution, adaptiveStrategy, projectionStrategy)
{
  // Nothing to do
}

/* Constructor */
FunctionalChaosAlgorithm::FunctionalChaosAlgorithm(const Sample & inputSample,
    const Point & weights,
    const Sample & outputSample,
    const Distribution & distribution,
    const AdaptiveStrategy & adaptiveStrategy,
    const ProjectionStrategy & projectionStrategy)
  : MetaModelAlgorithm(inputSample, weights, outputSample, distribution)
  , adaptiveStrategy_(adaptiveStrategy)
  , projectionStrategy_(projectionStrategy)
  , maximumResidual_(ResourceMap::GetAsScalar( "FunctionalChaosAlgorithm-DefaultMaximumResidual" ))
{
  // Overwrite the content of the projection strategy with the given data
  projectionStrategy_.setMeasure(distribution);
  projectionStrategy_.setExperiment(FixedExperiment(inputSample));
  projectionStrategy_.setWeights(weights);
  projectionStrategy_.setInputSample(inputSample);
  projectionStrategy_.setOutputSample(outputSample);
}


/* Virtual constructor */
FunctionalChaosAlgorithm * FunctionalChaosAlgorithm::clone() const
{
  return new FunctionalChaosAlgorithm(*this);
}


/* String converter */
String FunctionalChaosAlgorithm::__repr__() const
{
  return OSS() << "class=" << getClassName();
}


/* Maximum residual accessors */
void FunctionalChaosAlgorithm::setMaximumResidual(Scalar residual)
{
  maximumResidual_ = residual;
}

Scalar FunctionalChaosAlgorithm::getMaximumResidual() const
{
  return maximumResidual_;
}

/* Projection strategy accessor */
void FunctionalChaosAlgorithm::setProjectionStrategy(const ProjectionStrategy & projectionStrategy)
{
  projectionStrategy_ = projectionStrategy;
}

ProjectionStrategy FunctionalChaosAlgorithm::getProjectionStrategy() const
{
  return projectionStrategy_;
}

AdaptiveStrategy FunctionalChaosAlgorithm::getAdaptiveStrategy() const
{
  return adaptiveStrategy_;
}

/* Computes the functional chaos */
void FunctionalChaosAlgorithm::run()
{
  const UnsignedInteger outputDimension = getOutputSample().getDimension();

  // Get the measure upon which the orthogonal basis is built
  const OrthogonalBasis basis(adaptiveStrategy_.getImplementation()->basis_);
  const Distribution measure(basis.getMeasure());

  // First, compute all the parts that are independent of the marginal output
  // Create the isoprobabilistic transformation
  // We have two distributions here:
  // + The distribution of the input, called distribution_
  // + The distribution defining the inner product in basis, called measure
  // The projection is done on the basis, ie wrt measure_, so we have to
  // introduce an isoprobabilistic transformation that maps distribution_ onto
  // measure
  //
  const DistributionTransformation transformation(distribution_, measure);
  transformation_ = transformation;
  inverseTransformation_ = transformation.inverse();

  // Build the composed model g = f o T^{-1}, which is a function of Z so it can be decomposed upon an orthonormal basis based on Z distribution
  const Bool noTransformation = (measure == distribution_);
  const Function model(DatabaseFunction(getInputSample(), getOutputSample()));
  if (noTransformation) composedModel_ = model;
  else composedModel_ = ComposedFunction(model, inverseTransformation_);
  // If the input and output databases have already been given to the projection strategy, transport them to the measure space
  const Sample initialInputSample(projectionStrategy_.getInputSample());
  if (!noTransformation)
  {
    LOGINFO("Transform the input sample in the measure space");
    const Sample transformedSample(transformation_(initialInputSample));
    projectionStrategy_.setInputSample(transformedSample);
  }
  // Second, compute the results for each marginal output and merge
  // these marginal results.
  // As all the components have been projected using the same basis,
  // the representation is a linear combination of selected multivariate
  // polynomials with vector coefficients
  // We build the coefficients of the combination. As some indices may be
  // missing, we have to take care of the different sparsity patterns
  std::map<UnsignedInteger, Point> coefficientsMap;
  const Scalar smallCoefficient = ResourceMap::GetAsScalar("DualLinearCombinationEvaluation-SmallCoefficient");
  for (UnsignedInteger outputIndex = 0; outputIndex < outputDimension; ++outputIndex)
  {
    LOGINFO(OSS() << "Work on output marginal " << outputIndex << " over " << outputDimension - 1);
    Indices marginalIndices;
    Point marginalAlpha_k;
    // Compute the indices, the coefficients, the residual and the relative error of the current marginal output
    runMarginal(outputIndex, marginalIndices, marginalAlpha_k);
    for (UnsignedInteger j = 0; j < marginalIndices.getSize(); ++j)
    {
      // Deal only with non-zero coefficients
      const Scalar marginalAlpha_kj = marginalAlpha_k[j];
      // To avoid -0.0
      if (std::abs(marginalAlpha_kj) > smallCoefficient)
      {
        // Current index in the decomposition of the current marginal output
        const UnsignedInteger index = marginalIndices[j];
        // If the current index is not in the map, create it
        if (coefficientsMap.find(index) == coefficientsMap.end()) coefficientsMap[index] = Point(outputDimension, 0.0);
        // Add the current scalar coefficient to the corresponding component of the vectorial coefficient
        coefficientsMap[index][outputIndex] = marginalAlpha_kj;
      }
    } // Loop over the marginal indices
  } // Loop over the output dimension
  // At this point, the map contains all the associations (index, vector coefficient). It remains to present these data into the proper form and to build the associated partial basis
  std::map<UnsignedInteger, Point>::iterator iter;
  // Full set of indices
  Indices I_k(0);
  // Full set of vectorial coefficients
  Sample alpha_k(0, outputDimension);
  // Full set of partial basis functions.
  FunctionCollection Psi_k(0);
  for (iter = coefficientsMap.begin(); iter != coefficientsMap.end(); ++iter)
  {
    const UnsignedInteger i = iter->first;
    const Point currentCoefficient(iter->second);
    I_k.add(i);
    alpha_k.add(currentCoefficient);
    // We could reuse the function
    Psi_k.add(basis.build(i));
  }
  // Build the result
  result_ = FunctionalChaosResult(inputSample_, outputSample_, distribution_, transformation_,
                                  inverseTransformation_, basis, I_k, alpha_k, Psi_k);
  result_.setIsLeastSquares(projectionStrategy_.isLeastSquares());
  result_.setInvolvesModelSelection(adaptiveStrategy_.getImplementation()->involvesModelSelection() ||
                                    projectionStrategy_.getImplementation()->involvesModelSelection());

  // set selection history
  Collection<Point> coefficientsHistory;
  Collection<Indices> indicesHistory(projectionStrategy_.getImplementation()->getSelectionHistory(coefficientsHistory));
  result_.setSelectionHistory(indicesHistory, coefficientsHistory);
  result_.setErrorHistory(projectionStrategy_.getImplementation()->getErrorHistory());
}

/* Marginal computation */
void FunctionalChaosAlgorithm::runMarginal(const UnsignedInteger marginalIndex,
    Indices & indices,
    Point & coefficients)
{
  // Initialize the projection basis Phi_k_p_ and I_p_
  LOGINFO("Compute the initial basis");
  adaptiveStrategy_.computeInitialBasis();
  do
  {
    LOGINFO("Compute the coefficients");
    projectionStrategy_.computeCoefficients(composedModel_, adaptiveStrategy_.getImplementation()->Psi_, adaptiveStrategy_.getImplementation()->I_p_, adaptiveStrategy_.getImplementation()->addedPsi_k_ranks_, adaptiveStrategy_.getImplementation()->conservedPsi_k_ranks_, adaptiveStrategy_.getImplementation()->removedPsi_k_ranks_, marginalIndex);
    // The basis is adapted under the following conditions:
    // + the current residual is small enough
    // + the adaptive strategy has no more vector to propose
    if (projectionStrategy_.getResidual() < maximumResidual_)
    {
      LOGINFO("Stop on small residual");
      indices = adaptiveStrategy_.getImplementation()->I_p_;
      coefficients = projectionStrategy_.getCoefficients();
      return;
    }
    LOGINFO("Adapt the basis");
    adaptiveStrategy_.updateBasis(projectionStrategy_.getImplementation()->alpha_k_p_, projectionStrategy_.getImplementation()->residual_p_, projectionStrategy_.getImplementation()->relativeError_p_);
  }
  // Check if there is still something to do
  while ((adaptiveStrategy_.getImplementation()->addedPsi_k_ranks_.getSize() > 0) || (adaptiveStrategy_.getImplementation()->removedPsi_k_ranks_.getSize() > 0));

  LOGINFO("No more basis adaptation");
  indices = adaptiveStrategy_.getImplementation()->I_p_;
  coefficients = projectionStrategy_.getCoefficients();
}


/* Get the functional chaos result */
FunctionalChaosResult FunctionalChaosAlgorithm::getResult() const
{
  return result_;
}

/* Method save() stores the object through the StorageManager */
void FunctionalChaosAlgorithm::save(Advocate & adv) const
{
  MetaModelAlgorithm::save(adv);
  adv.saveAttribute( "maximumResidual_", maximumResidual_ );
  adv.saveAttribute( "result_", result_ );
}


/* Method load() reloads the object from the StorageManager */
void FunctionalChaosAlgorithm::load(Advocate & adv)
{
  MetaModelAlgorithm::load(adv);
  adv.loadAttribute( "maximumResidual_", maximumResidual_ );
  adv.loadAttribute( "result_", result_ );
}



END_NAMESPACE_OPENTURNS
